The present disclosure generally relates to heat transfer labels, and more particularly to heat transfer labels with reduced halo and a method of making the same.
Heat transfer labels are well known and used in various industries. For example, heat transfer labels are widely used in apparel industries. Heat transfer labels are often screen printed using solvent based inks Typically, heat transfer labels require an adhesive layer to attach the label to a substrate. For example, apparel labels typically include an adhesive layer having a thickness of about 50-100 micrometers or thicker to provide adequate adhesion between the label and a textured surface of garments to which they are applied. Such a thick adhesive layer often requires several screen printing passes to achieve the desired thickness.
Thus, it is not unusual for the adhesive component to make up 80-95% of the total volume of a heat transfer label. Adhesives for screen printed apparel labels are usually prepared as a dispersion of an insoluble hot melt adhesive powder in a compatible solution of resin and solvent. Thus, the adhesive component, which makes up a substantial volume of the label, often is responsible for the majority of volatile organic compounds (VOC) associated with the printing of the label. Further, a relatively thick layer of adhesive printed using a solvent based adhesive ink can retain solvent, causing undesirable odors when the label is applied.
In addition to VOC and multiple printing passes required to provide an adequate thickness of the adhesive layer, screen printed heat transfer labels also exhibit an undesirable “halo”. Different printing presses and methods have a different “color to color tolerance” associated with a particular printing press and/or method. This tolerance is determined by the press movements, which are inherent in the printing equipment. To accommodate the “color to color tolerance” of a screen printing process, an adhesive layer of a heat transfer label is printed larger than graphic layers to ensure that the adhesive layer is behind all of the graphic layers. For example, if the “color to color tolerance” of a screen printing press is ±0.25 mm, under optimum conditions, there will be an even border of adhesive extending 0.25 mm around the entire graphic layer. Under some less optimal conditions, there will be an uneven border of adhesive, for example, some parts extending more than 0.25 mm beyond the graphic layer and some parts with nearly no adhesive border. Thus, the adhesive layer is sized according to the tolerance of the particular equipment and/or printing method to ensure that the adhesive layer is behind the entire graphic layers even in the worst expected conditions, such that the label can be applied to a substrate successfully. However, such an adhesive border creates a “halo” around the graphic portion of a label, which is visible on the substrate after the label is applied. Many end users find these adhesive halos aesthetically undesirable.
Efforts have been made to develop alternative printing methods to reduce VOC from solvent based printing methods. For example, extrusion coating and powder coating methods use solid powder adhesives without a solvent. In extrusion coating, a layer of adhesive is extruded over graphic areas. However, this method does not address the “halo” effect, because a layer of adhesive, which is applied across the entire support film covering graphic areas and open areas between the graphic areas, creates a “halo” that may be even larger than that of one produced by screen printing.
In powder coating, a powder adhesive is applied over the last wet ink pass, and the powder coated surface is brushed to remove the powder adhesive that did not stick to the wet ink. Subsequently, the powder adhesive coated label is heated to melt and distribute the adhesive. Thus, in theory, only the adhesive particles that are adhered to the wet ink remain on the label, and thus, no adhesive “halo” will be created with this method. However, this will only work for labels that have all the graphics backed with one backer color, since it requires a wet pass of ink to hold the powder in place before the fusion step. Thus, if the entire label is backed by a white ink, for example, the powder adhesive can be applied over the entire graphic label without an adhesive “halo”. However, for labels including different backer colors for different portions of the graphic label, an extra clear coat must be applied as the last print pass to provide a wet ink surface for the powder to adhere. However, such a clear backing will create a “halo” similar to the adhesive “halo”. Further, powder coating can be messy and pose difficulties in maintaining a clean manufacturing environment.
Accordingly, there is a need for improved heat transfer labels and a method of making the same, in which the “halo” is minimized and VOC is reduced.